package summer_vacation.liqing;

/**
 * Created by 123456 on 2015/8/7.
 */
public class Java45 {
    public static void main(String[] args) {
        double sum = 0, a = 1;
        int i = 1;
        while (i <= 20) {
            sum = sum + a;
            i = i + 1;
            a = a * (1.0 / i);
        }
        System.out.println(sum);
    }
}
